Internal plasticization of chitosan with oligo(DL-lactic acid) branches

To enhance the mechanical properties of chitosan without impairing its biological properties and rendering it a more flexible and pliable material, oligo(lactic acid) branches were inserted in a systematic way onto the polymer's backbone. Six grafted copolymers were prepared and thoroughly characterized using chemical means, Dynamical Mechanical Thermal Analysis (DMTA), and Solid State Nuclear Magnetic Resonance (SSNMR, CPMAS and SPMAS). The degree of insertion and the length of the pendant groups were determined. The resulting morphology and mechanical properties demonstrated that the branching introduced strong modifications on the dynamic behavior of the pristine chitosan, and consequently on the mechanical properties of the composite materials a whole. The method described makes it possible to design homogeneous chitosan based materials with good mechanical properties, including a desired degree of flexibility. The results demonstrated that the degree of plasticization of chitosan can be achieved by proper control of the oligo( dl -lactic acid) branching.